[xen staging] compilers: always use _Static_assert with clang

[patchbot@xxxxxxx]

commit 3d5a836379e5064d563322de095d0775607ff185
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Jun 2 13:39:02 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 2 13:39:02 2020 +0200

    compilers: always use _Static_assert with clang
    
    All versions of clang used by Xen support _Static_assert, so use it
    unconditionally when building Xen with clang.
    
    No functional change expected.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Wei Liu <wl@xxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Paul Durrant <paul@xxxxxxx>
---
 xen/include/xen/lib.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index e5b0a007b8..076bcfb67d 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -25,7 +25,9 @@
 #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
 #define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
 
-#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
+/* All clang versions supported by Xen have _Static_assert. */
+#if defined(__clang__) || \
+    (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))
 /* Force a compilation error if condition is true */
 #define BUILD_BUG_ON(cond) ({ _Static_assert(!(cond), "!(" #cond ")"); })
 
--
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